This invention relates to polymeric emulsions. In another aspect, this invention relates to the formation of high solids polyethylene emulsions directly by emulsion polymerization.
Stable polyethylene emulsions are conventionally utilized as components within surface treating and coating compositions such as lacquers, paints and polishes. Improved polyethylene emulsions are made with the use of water soluble persulfate catalysts and nonionic and fatty acid type anionic emulsifiers in U.S. Pat. No. 3,226,352 and U.S. Pat. No. 3,244,625, respectively. Such improved emulsions are formed by polymerizing ethylene in an aqueous medium to a relatively low solids level and later concentrating the product emulsion to a relatively high solids level.
Furthermore, improved stable emulsions of polyethylene have been produced utilizing a persulfate catalyst and an alkyl aryl sulfonate type emulsifier by the process disclosed in U.S. Pat. No. 3,352,807. According to the process of U.S. Pat. No. 3,352,807 the water soluble persulfate initiator is present in concentrations of less than about 0.5 weight percent of the reaction medium and up to about 5 weight percent of the reaction medium of an alkyl aryl sulfonate emulsifier system which comprises at least 50 weight percent of an emulsifier which contains at least one alkyl group which is attached to the aromatic ring through a secondary or tertiary carbon atom. The latexes produced in accordance with this process are stable and are generally produced at a solids level of from about 17 to 20 weight percent and then later concentrated to a solids content of from about 40 to about 55 weight percent.
Thus, the processes for producing stable polyethylene emulsions generally include the formation of an initial emulsion in a reaction zone and thereafter a concentration step such as carried out in a conventional concentration unit such as a falling film evaporator preferably operated under vacuum to strip a portion of the liquid phase therefrom and form a polymer emulsion at a higher solids level.